A great deal of damage is done to higher plants, including crop plants, by pathogenic organisms. Plants are known to have certain natural defenses against pathogens. However, there is often an inability of the plants to recognize the pathogen to cause the defenses of the plants to be induced.
There is great economic loss caused by pathogenic attack against higher plants in which the natural defenses of plants are inadequate or fail to respond and defend the plants against damage by pathogens.
As used herein, the term "higher plant" refers to a multicellular differentiated organism that is capable of photosynthesis, such as angiosperms and multicellular algae. The term does not include microorganisms, such as bacteria, yeast, and fungi. The term "plant cell" includes any cell derived from a plant; this includes undifferentiated tissue such as callus, as well as plant seeds, pollen, or plant embryos.
It is known that higher plants have a general plant defense mechanism against plant pathogens. At the present, the mechanism that triggers the activation of plant defense mechanisms and induces systemic resistance is not known. It is known that pathogenic attack can cause in plants the synthesis of high levels of Pathogenesis-Related (PR) proteins. Among these, PR-1 is usually synthesized in response to viral attack; PR-2 encodes a .beta.-1,3-glucanase, which may serve as an anti-bacterial/fungal enzyme; PR-3 encodes an anti-fungal enzyme, chitinase (Linthorst, 1991); Phenylalanine ammonia-lyase (PAL), a key enzyme in the phenylpropanoid pathway that is involved in the biosynthesis of phenolic compounds (Bowles, 1990).
Transgenic plants of this invention contain much higher levels of PR proteins and salicylic acid (SA) than corresponding wild-type plants, and accumulate UV-fluorescence compounds (accumulation of UV fluorescence compounds is a well documented anti-microbial process that is part of the plant defense mechanism). Higher endogenous levels of SA are known to function as a signal for systemic acquired resistance against a broad spectrum of pathogens (including virus, bacteria and fungi) in plants. Upon challenge with viral and bacterial pathogens, it has been found that the transgenic plants provided by this invention show heightened disease resistance, similar to systemic acquired resistance.
The following is a list of designations used herein and the designations have the following definitions:
bO gene--bacterio-opsin gene PA0 Cab-t--chlorophyll a/b binding protein transit peptide PA0 GUS--.beta.-glucuronidase coding region PA0 HR--Hypersensitive Response PA0 NOS--nopaline synthase gene PA0 .OMEGA.--synthetic omega translation enhancing sequence PA0 PCR--polymerase chain reaction PA0 PR--Pathogenesis Related Proteins, for example, PR-1, PR-2 and PR-3 PA0 SA--salicylic acid PA0 SAR--systemic acquired resistance PA0 TMV--tobacco mosaic virus PA0 TNV--tobacco necrosis virus PA0 WT--wild-type plants (plants which are not transgenic)